Problems with making a speaker from scratch

[ENIAC]

I've been watching these videos online on how to make a speaker with a plastic bowl a coil and a magnet. Never knew it was really that simple, pretty amazing. Anyways, I just got my neodymium magnets today and tried this out but I have a problem with soldering. The small pieces of copper wire I have wrapped around a small piece of cardboard won't allow the solder in. However, the 3.5mm wire that I am going to use to go to a speaker solders just fine, it soaks the stuff right up. It's just trying to tin the two coil leads to the 3.5mm is proving nearly impossible. I am using .050" Diameter 60/40 rosin-core solder from radioshack. Any ideas what I might be doing wrong here or why this isn't working. And what would you suggest the for the number of turns for an inch in diameter and inch in height piece of cardboard? Is there an equation for this?


Thank you

[Yago]

Remove the coating on the wire at the ends, just enough to solder too.

[ENIAC]

I did, I scratched them off with a razor blade then used a lighter to get the enamel all the way off. Still not working 

[IanB]

See this video:

http://youtu.be/Pd5Q-XDmvys

I can attest from personal experience that the information given is sound.

If it doesn't work either your wire is bad or your technique is wrong.

(Just in case there is something crazy going on here, make sure the cleaned wire is reddish like copper and not silvery like aluminium. If it happens to be aluminium it cannot be soldered.)

[ENIAC]

Oh! it is silvery   ....I got the coil off an old speaker, why would the old speaker use aluminium wire instead of copper? The enable is like a bright almost orangish color. I shave off the first layer it's silver metallic. I had to force the solder on there because I just wouldn't stick I got a glob of it on top of the copper speaker wire and it sorta stuck. But the solder on the wire is like brownish black? is that normal?

[Yago]

Good question on the use of aluminium for speaker coil IDK that one.

The brown look of the solder is the flux that has burnt, this means the flux got too hot and knackered during soldering.
I don't think that is your problem here, but not something that will help a good solder joint form at all.
Something to work out along the way, watch Dave's soldering vids.

You could get some enamelled copper wire form an old transformer, have a look in some old broken mains powered electronics/power supplies.

[ENIAC]

How many turns of copper would I need for a 1 inch in diameter and 1 inch in height piece of cardboard for this speaker? If you could provide an equation that would be great!

[IanB]

From memory, if you take apart a real loudspeaker you tend to find a single layer coil with as many turns of very fine wire as will fit.

The size of the cardboard cylinder should be according to the size of the magnet. It needs to be as close to the magnet as possible so that it can still move freely without snagging.

If you want 1 inch in diameter, that implies a magnet that is also 1 inch in diameter. And for a neodymium magnet that would be a huge and very dangerous magnet. What size magnets do you actually have?

[denelec]

Aluminium is much lighter than copper. 
It makes sense in a speaker voice coil.
Soldering aluminium is difficult.  You will need a special flux. 

[ENIAC]

@IanB The neodymium magnets are 1/2" in diameter and 1/2" in height.


@denelec is aluminium as conductive as copper?


I'm just going to put voice coil off to the side. I keep having these projects after project fail and then they pile up in a corner of my room until I have a better understand to make them work...I need to make this one work. It's perfect for the beginner level.

[IanB]

The voice coil is not an experiment I have tried. But if your magnet is 1/2" in diameter, you should make a paper cylinder the same size as the magnet by wrapping paper loosely round it. Them make your coil by wrapping as many turns of thin magnet wire around the cylinder as you can in a single even layer. Use tape to hold the wire in place. You don't really have to solder to the ends of the magnet wire. Just leave very long tails and clip onto the ends with alligator clips.

[atferrari]

I did, I scratched them off with a razor blade then used a lighter to get the enamel all the way off. Still not working 

Razor blades? Wow!

Looking for them, here it is impossible to get some even if as collectibles.

[SeanB]

Razor blades? Wow!

Looking for them, here it is impossible to get some even if as collectibles.

Go to China store, they will have them somewhere. Gillette, Minora, all copies but still sharp and usable.

[Yago]

Aluminium is much lighter than copper. 
It makes sense in a speaker voice coil.
Soldering aluminium is difficult.  You will need a special flux. 

Cheers, didn't think about the weight, makes sense.

I did have a go at winding a voice coil, as said cardboard tube, I used a light coat of varnish to secure the coil after I wound it.
Also , if you wind it whilst in place on the magnet, might be a good idea to put some grease proof paper between magnet and tube as a shim, if the coil pulls the tube in tight and binds, removing the shim gives you back some clearance.

[denelec]

@denelec is aluminium as conductive as copper?

No, aluminium is about 1,7x more resistive than copper.
http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

So for the same resistance per meter, you will need a bigger wire.
But since aluminium density is 3,3 times less than copper, even with a bigger wire, you will still have less weight.

[ENIAC]

Oy vey...
So I went to sleep with my laptop and magnet on the bed....seems it must have rolled near my laptop and "poof" harddrive is wiped. Lesson learned...had to shell out 150$ to get it replaced. It's not like I didn't know this fact but wow I can't believe this happened, I was being careless. Those neodymium magnets are nothing to toy around with.

School just started back up for me. However, along studies I want to complete this. So I shall get a cardboard with the diameter and height a little more than the actual magnet. I will post pictures when complete maybe even a video.

[IanB]

a huge and very dangerous magnet

it must have rolled near my laptop and "poof" harddrive is wiped

Well, oops